Field of the Invention
The present invention relates to a surge protective device (hereinafter, referred to as an “SPD”) for communication for protecting equipment to be protected such as communication equipment and control equipment against intrusion of lightning surge, and a surge protective system in which a plurality of SPDs for communication are installed together.
Description of the Related Art
Conventionally, for example, Japanese Patent No. 5778541 and U.S. Pat. No. 8,730,638 B2 disclose an SPD for power supply for protecting equipment to be protected such as power supply equipment against intrusion of lightning surge, and a surge protective system in which a plurality of SPDs are installed together.
The conventional surge protective system includes a plurality of SPDs which are installed together, and a monitor unit which displays degradation states of the plurality of SPDs and which supplies power supply voltages to the plurality of SPDs. The bottom faces of the plurality of SPDs and the bottom face of the monitor unit are detachably attached to, for example, a mounting rail for devices. A sensor unit for detecting intrusion of lightning surge at each SPD and the monitor unit are connected through a power cable for supplying a power supply voltage and a communication cable for transmitting a communication signal. Power is supplied from the monitor unit to each SPD, and lightning surge detection data is transmitted from the sensor unit of each SPD to the monitor unit through the power cable and the communication cable.
However, the conventional surge protective system has the following problems of (A) to (C).
(A) Problem of Workability
In the conventional SPD, a connection of the power cable and the communication cable is embedded into a bottom face side of the sensor unit. Therefore, it is necessary to lay the power cable and the communication cable, for example, in a state where the SPD body is detached from the mounting rail for devices, which leads to poor workability.
(B) Difficulty in being Used in a Communication System (that is, Used as an SPD for Communication)
When the conventional SPD is used in lines of a power system (that is, used as an SPD for power supply), because it is only necessary to provide two or three connections of SPDs, there needs to be less points where the power cable and the communication cable are laid, which does not take a lot of troubles for work. However, when the conventional SPD is used in a communication system, because the number of lines is extremely larger than that of the power system (for example, several tens to several hundred lines may be required), there needs to be an extremely large number of connections of the SPDs, which makes it difficult to lay the power cable and the communication cable.
(C) Difficulty in Annexing Work
Work of annexing an SPD is difficult because it is necessary to extend the power cable and the communication cable from those already provided.